Sensors generally measure a physical quantity and convert the measured physical quantity into a signal that is provided to an electronic instrument (e.g., integrated chip processor). For instance, magnetic sensors measure a magnetic field using one or more magnetic field sensor elements sensitive to magnetic fields, and output an electric signal (e.g., voltage signal or current signal) corresponding to the measured magnetic field.
A sensor package may also include a signal processing circuit that receives the signal (i.e., sensor signal) from the magnetic field sensor element and derives, from the sensor signal, a measurement signal. Therefore, a sensor package can include a magnetic field sensor and a circuit which conditions and amplifies the small signal of the magnetic field sensor via signal conditioning.
Magnetic field sensor elements typically have either limited magnetic sensitivity or limited bandwidth. For example, a Hall plate has moderate magnetic sensitivity of 50 mV/V/T and its bandwidth is limited to 30 kHz due to eddy currents in the leadframe of a leaded package, or it is limited to a bandwidth of 150 kHz due to the signal conditioning circuit in the package. For example, the signal conditioning circuit may be a spinning Hall probe circuit, which is a time discrete circuit operating at a chopper frequency of 50-500 kHz.
In addition, the above magnetic field sensor elements are resistive devices having typical resistance of a few kilo-ohms, which creates a large amount of noise at high frequencies (e.g., in the MHz range). This further restricts the frequency at which these sensor elements can be operated.
An on-chip coil disposed on a surface of a semiconductor chip may also be used as a magnetic field sensor element. The on-chip coil may have large bandwidth if it is not mounted near a conducting plate, such as the leadframe. However, the on-chip coil has only limited magnetic sensitivity because its effective area is small due to the small size of the semiconductor die (e.g., in the order of a few square millimeters) and the number of turns is also limited to 10-1000 because there are only a few metallization layers available in commercial micro-electronic processes.
In view of the above, current magnetic field sensors have a limited signal-to-noise ratio (SNR) at large bandwidths.